Work vehicles are configured to perform a wide variety of tasks for use as construction vehicles, forestry vehicles, lawn maintenance vehicles, as well as on-road vehicles such as those used to plow snow, spread salt, or vehicles with towing capability. Additionally, work vehicles such as a bulldozer, may be equipped with bulldozer blades for pushing dirt and other materials. It is desirable to adjust the position the blade for different operations and conditions. On utility crawler dozers, the blade is typically adjustable in different directions, which includes raising and lowering of the blade, adjusting a pitch position of the blade by moving the top portion of the blade forward and backward relative to a lower pivot point, and an angle of the blade by moving the blade left or right about a center pivot point.
Currently, a hydraulic control valve is used to raise and lower the blade. A spool valve is shifted to direct oil flow to each side of a hydraulic cylinder coupled to the frame and to the blade. A quick drop valve is plumbed in series with the spool valve, and when an operator desires to lower the blade quickly, the quick drop valve is activated to connect the rod end of the cylinder (return flow during lower) to the head of the cylinder.
The quick drop valve is an on/off valve that connects both ends of the cylinder together to regenerate oil and to provide a fast drop speed. On a crawler dozer, the blade lower function is usually the highest velocity function. The blade lower return flow usually ends up dictating the control valve size and is a limiting factor. The rapid descent of the blade, however, generates undesirable forces on the quick drop valve and the hydraulic cylinder that can reduce the life of these devices as well as increase the amount of repair and maintenance required to maintain the blade adjustment system. This rapid descent also increases the likelihood of cavitation which can damage the quick drop valve and cylinders. What is needed therefore is position control system and method for an implement of a work vehicle to reduce and/or eliminate damage and repair costs to implement lowering systems.